Coho Salmon, Ocean Fish breeds in fresh water introduced to Great Lakes
Coho Salmon, Ocean Fish breeds in fresh water introduced to Great Lakes

Michaela Moore, UW-Milwaukee First Year Biology Major  

What do fish breathe?

Fish breathe oxygen, much like humans. However, fish don’t breathe air like humans do, they breathe the oxygen that is dissolved in the water. They don’t breathe oxygen in its molecular form H2O) though, they breathe oxygen as a gas (O2.). (Cary Institute of Ecosystem Studies)

How do fish breathe?

Fish breathe through their gills, which are the feathery slits on the sides of their bodies. Fish will take water in through their mouths, then as the water is being pushed out through the gills, the dissolved oxygens in the water will absorb into all the tiny blood vessels which then travel throughout the fish’s body through the bloodstream. (National Center for Families Learning)

What processes increase oxygen levels in the water?

There are a few processes that increase dissolved oxygen levels in the water. The first is the temperature. When the water is cooler, typically in the winter months, it has the capability of dissolving more oxygen into the water. When the air is cold, the water in the stream or river tends to move a little faster which increases the interaction between the water and the air, thus increasing the level of dissolved oxygen. Most rivers and streams have sections with a lot of rocks that provide aeration for the water. When the water quickly flows over those rock beds, it acts as a little waterfall and allows more dissolved oxygen in the water and increases its concentration. During the day, the plants in the water undergo photosynthesis, which is the absorption of  light energy by the plant from the sun which turns that energy into oxygen that is released from the plant into the water. Bodies of water with more plants tend to have very high dissolved oxygen concentrations during the day when photosynthesis is occurring. (Shifflett, Shawn Dayson)

What conditions lower the oxygen level in water?

There are actually a lot of conditions that lower the level of dissolved oxygen in the body of water. The main one is the temperature. When the water is warm, the dissolved oxygen concentration is much lower than when the water is cold. A lot of times too, rivers and streams that flow at a slower pace have warmer water and lower dissolved oxygen concentrations. At night, the plants in the water undergo respiration, where they take oxygen out of the water and use it for energy. This vastly lowers the dissolved oxygen concentration of the water, however, this only occurs at night so the next day there will be plenty of photosynthesis occurring to bring the concentration back up. Oxygen dissolves the best in water that has a low level of solids and decaying plant material. This is because bacteria use a lot of energy and oxygen to decompose these materials. The more solids and organic matter in the water, the more bacteria will be needed to decompose these materials, therefore, a lot of these materials in the water will significantly lower the dissolved oxygen concentration. Also, areas where sewage gets dumped into the water have a low dissolved oxygen concentration because the sewage brings a lot more bacteria in the water which use more oxygen. Even the amount of nutrients in the water can negatively effect dissolved oxygen concentrations. This is because when there are more nutrients in the water, that tends to create more algae in the water. When there are algae, bacteria are needed to decompose it. Having more algae requires more bacteria which use more oxygen to decompose the algae, thus more algae in the water lowers the dissolved oxygen concentration. (Shifflett, Shawn Dayson)

What are the major game fish in the Milwaukee River?

The most abundant fish in the Milwaukee River are the Coho and Chinook salmon. Brown trout and rainbow trout are also very abundant, as well as smallmouth bass. There has been much effort toward increasing the level of walleye in the river as well, since the levels of walleye have been declining in recent years. (Wisconsin DNR)

What is the life cycle of a Coho salmon?

The life cycle of the Coho salmon is similar to the life cycle of just about any fish. The female salmon will lay her eggs in a gravel bed, where the eggs won’t float away and are easily camouflaged by the rocks. The male salmon will then fertilize the eggs and they will rest there throughout most of the winter months, hatching in late winter. Once they hatch, they move into the alevin stage of life, which lasts about four months. This is when the salmon look the weirdest, as they have large eyes and a very straight, skinny body. After the four-month alevin stage, the young salmon become a fry. Typically in the fry stage, the salmon will be about an inch in length and are free swimming. The young salmon will stay in the fry stage for about 3 years, staying in slow moving streams and rivers. The salmon will then move out of the fry stage and become a smolt. This means that the salmon is ready to migrate to the ocean until it becomes an adult Coho salmon. It usually takes about 18 months for the adult salmon to mature. Once mature, the female salmon will migrate back to where she was originally a salmon egg. Once she reaches her place of origin, she will lay her eggs and die soon after. This continues the salmon life cycle all over again. (Wild Pacific Salmon)

What is the life cycle of a dragonfly, what do they eat, and what eats them?

There are three stages to the life cycle of a dragonfly. The first stage of their life begins as an egg. While flying together, the male and female dragonflies will mate together. The female will then lay her eggs on a plant in the water unless one is not available, in which case she will just drop her eggs in the water. After the dragonfly eggs hatch, the nymph stage of their life begins. The nymph stage is the longest stage of the life cycle of a dragonfly, and most dragonflies will live most of their life in this stage. During that stage, the dragonfly larvae will live in the water for up to four years. If the nymph stage of the life cycle is complete at the beginning of the winter season, the dragonfly will stay in the water until the following spring when the water warms enough for it to come out. Because waters are calmer, the dragonfly nymphs live in marshy areas or ponds instead of quicker moving rivers or streams. Cannibalism is a trait of the dragonfly nymphs, as they will eat smaller dragonfly nymphs as food. Once the nymph stage is complete, the dragonfly will exit the water on the stem of a plant where it will shed its skin. Once the skin of the dragonfly is shed, the dragonfly is considered a full grown adult, a period of time that usually lasts about two months. The hunt for a mate begins and the female dragonfly will begin to look for a calm body of water to lay her eggs. (Dragonfly Site)

Dragonflies can eat up to their own body weight in about a half an hour. As nymphs, typically their diet consists of other insects including mosquito larvae and other aquatic insects. They will also eat worms and sometimes even tadpoles or small fish. Once the dragonfly has grown into an adult and left the water, they will eat many small insects including mosquitoes, gnats, mayflies, flies, and other small insects. Occasionally they will eat a butterfly or a bee to change up their diet. (Dragonfly Site)

Fish and frogs are a big portion of what eat dragonflies as both larvae and adult dragonflies. Birds also feast on dragonflies, but typically eat them when they are metamorphosing from nymphs into adult dragonflies. Spiders will capture adult dragonflies in their webs and eat them, while wasps will sting the dragonfly and lay their eggs on the paralyzed insect to let their larvae feed on in. During the dark times of the night, bats will find dragonflies out and about and eat them. Sometimes even dragonflies will eat other large dragonflies, while smaller dragonflies will eat mostly damselflies. (Burchsted, Albert)

Works Cited: Burchsted, Albert. (December 11th, 2013). What Dragonflies Eat and What Eats Them. Retrieved from

Cary Institute of Ecosystem Studies. (n.d.). Dissolved Oxygen. Retrieved from

Dragonfly Site. (n.d.). What do dragonflies eat? Retrieved from

Dragonfly Site. (n.d.). The Dragonfly Life Cycle. Retrieved from

National Center for Families Learning. (n.d.). How do fish breathe underwater? Retrieved from

Shifflett, Shawn Dayson. (n.d.). Water and Sustainability. Retrieved from

Wild Pacific Salmon. (2007). Wild Coho Salmon. Retrieved from

Wisconsin DNR. (October 2005). Milwaukee River Estuary Walleye Management Plan. Retrieved from